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I have a five year old Weil McClain WGO 3 oil fired hot water boiler, in my new cape home that was built in 2000. It will heat only to 66 on one zone when it gets below -30. To get it to 70 I have to crank the wall thermostat to 85 at 7 am and by 9 pm it will be 70 and slower keep going over 70. Then i can turn it down to 73.This is on the first floor which is on one zone. Home is about 40' by 40'. I have boiler set to 210 high limit. Should I cut the one zone 70 feet in half? The upstairs zone 30 feet works great if i turn it to 75 in minutes it that temp. Could the wall thermostat be bad? The technicians can't find anything wrong with the boiler. The heat lost came out OK, BTU's are three times the size it needs to be for my home (for later expansions) and there are enough registers. Weil McClain said its ok to set the 210. There are two shut off valves in the cellar. The technicians bleed the lines three different time over the the years. There is no noise like when there's air in the lines.
It's base board heat, ten feet long under all windows there 1" off the floors and about 6 inches in height. They each have one 3/4" pipe going in one side.There is only one water valve for each zone which is above each circular valve, next to the boiler. The two circular ( two zones one on each floor) valve sound the same ( very quiet) when running. I was thinking I may switch them to seem if one is bad, what do you guys think? The water maker that is next to the boiler works great. We never run out of hot water. Boiler runs at 15 psi and starts at 190 then stops at 210 degrees. It runs for 10 minutes 3 times per hour. So if the pump is good should i replace it with a multi speed pump first?
I just checked the water temperature at the boiler zones with a cheap meat thermo.( ZONE 1 IS THE PROBLEM WITH ONLY HEATING TO 66 DEG.) At zone 1, with 70 feet of base boards which is on the first floor, just above the boiler. At the beginning of this zone I got 162 to 190 degrees at the end I got 134 to 154 degrees by the circular pump. Pumps are 1/25 hp. Right know it set to 73 and heats to 70, temp outside is 0. This zone has never worked correctly .
Any other ideas guys?
Thanks,

I think you don't have enough baseboard on first floor or it is blocked with furniture or dampers are shut on baseboards. For one thing you mentioned the boiler only cycles 3 times per hour 10 minutes each cycle on a 0 degree F. day.
Another thing you mentioned the thermostat set at 85 slowly climbs to 73 but takes all day. This would indicate that the thermostat is attempting to get to its setpoint but the cold air infiltration is too much.

Most people don't size baseboard for -30 temps.
At least where I live a new construction house is sized for 0 degree temps.
On these very cold days most people have a propane decorative fireplace or stove, or pellet stove or wood stove.
I have plastic sheeting on the inside of my cheapo construction grade double pane windows. But I live in a small 1000 sq. foot 1940 year cape. Not much room for a space heater.

You could always split the first floor into 2 zones and add additional baseboard as a last resort if indeed you don't have enough baseboard. That is if room will allow it.
Adding to the one zone only on the first floor wouldn't help because the temp of the baseboard at the end of the run would be luke warm.

If its only that cold for a few weeks out of the year I would opt for a vented decorative stove installed this spring and put on a sweater in the meantime.

Are you sure the first floor zone is getting hot? At 210° it should burn to the touch. I would never run a boiler that close to to the temp of steam. 70 ft is about max for a single loop @ 3/4". That much BB should put out over 40K BTU when over 180°. I asume a 5 yr old house was well insulated, but I would check the calcs again at a -30° design point. Is the top floor that much smaller that is heats up fine with less then half the baseboard? A 3 section WGO can only make 100K BTU.

zone on oil boiler

I was wondering if you have balancing valves on this system? Many times they are installed and never set. I did see on one occasion where the velocity of the water traveling through the baseboard was so fast that it was unable to transfer any heat.

Right load and equipment summary for northeast

I just got a copy of the heat loss.I'm tring to figure it out. I see its calculated for -23. It says building heat loss is 51569 btu and design heat load is 51569. Infiltration area is 1783,
volume 14264,
air change per hour is .80,
equiv. AVF (cfm) 190.
Heating equipment summary-
efficiency 80.0 AFUE,
low output baseboard 590 BTU/ft,
total low baseboard 87 feet,
high output baseboard 730 btu/ft,
total high baseboard 71 feet.
Also has a cooling section for summer.
*We have no a/c setup.

The 134 deg to 154 deg brings up a big red flag for me.The output of radiant baseboard will drop off expotentially as you go below 180 deg.It sounds like you may have a zone with too much baseboard on one loop.

problem with a zone

Originally posted by markwolf The 134 deg to 154 deg brings up a big red flag for me.The output of radiant baseboard will drop off expotentially as you go below 180 deg.It sounds like you may have a zone with too much baseboard on one loop.

Thanks, the problem zone starts off at 190 degrees and drops to 134 after 70 feet of registors. What should it be at the pump return, about 40 degrees less or 150? I will check the return for the good zone.
EDIT: The good zone goes from 100 to 172 degrees at the return above the ciculator pump. This good zone is on the second floor and has 25 feet and half the heating area. The boilor is in the ceilor. Why is the return on the first floor 154 while the top floor return highest temp 170?

You are at about the limit of the 007, if its the black oem that came with the boiler that is your problem. The oem has a cheaper impellar then the green after market one.
Your baseboard btu is at a 4 gpm flow, your not getting.